The wifi is useful to me, but the 3g is really good. I will often be on a walking tour where all my battery charging is done by solar chargers except for one night in three or four where I will be in a bed and breakfast or similar, and the only internet I have will be 3g. So the kindle is really good with low battery use and internet most places for the " must have " book!

I buy mainly from Amazon but prefer to 'liberate' my ebooks so usually sideload and only rarely have them sent wirelessly. I do download the odd free book directly to my Kindle though. And despite showing my Mum how to keep her ebooks on her computer and load them onto her Kindle, she uses the WiFi all the time as it's far quicker and easier for her.

For sheer speed and ease of use, the combination of Amazon, Kindle & WiFi is very, very good.

I also liberate paid content, but find it quite simple to move/copy ebooks from my Kindle to Calibre for this purpose, so when new content is coming from Amazon, I use Wi-Fi or 3G to download directly to the device. Part of this is convenience: my Kindles live upstairs by my bed while my PC sits downstairs. I batch liberate, tag and otherwise organize my content via USB from my Kindles to Calibre about once a month. The rest of the time, I only turn on the Kindle radios when I know something new is coming from Amazon, or some news via Calibre and email.

Well, not invariably. I have a cheap data plan for my ipad for when wifi is not available and quite a lot of data (measured in gigabytes, but it does get slowed down after the first five) as well as unlimited voice on the phone. Anything I get from Amazon via 3g to my kindle I already paid for when I got the kindle. So I might as well use it, if I don't I won't be getting a discount.

I dont download anything over 3 G cos it costs! Altho Im usually only downloading game updates, which measure in MB not KB!

Some background info for you, because this is unique to Amazon:
The way the 3G kindles work is: they are a bit more expensive to purchase, but for the rest of their "life", you can browse the store or get books delivered via 3G for free. There is a limit as to how large the books can be - 2MB if I recall correctly. Anything over has to be downloaded via Wifi.
Even if you buy a used 3G kindle on Ebay, the 3G downloads are still free of charge.

I dont download anything over 3 G cos it costs! Altho Im usually only downloading game updates, which measure in MB not KB!

These days, most smartphones come with a data plan of some sort. Even if you had a data allowance of, say, 250MB/month (which is rather small), a 200kb ebook download would be using less than one thousandth of your monthly data allowance. It's really not "crazy" to download ebooks over 3G.